Field of the Invention
The present invention is directed to a method and device for converting Volatile Organic Compounds (VOC) into energy. More specifically, the invention relates to a method and device that concentrates a dilute hydrocarbon gas using a concentrator into a gaseous or liquid concentrated fuel. The concentrated fuel is then converted into a reformate using a reformer and converted into energy through an energy conversion device.
Background of the Invention
Various manufacturing, agricultural, contamination remediation and industrial processes produce a waste gas stream having dilute hydrocarbon concentrations. Some applications include those where the VOC is entrained in a solid or liquid media such as contaminated soil or water. The VOC can be converted to gas and separated from the solid or liquid media. Other processes produce or contain gaseous VOC. A number of processes exist to burn or oxidize the VOC, but the present invention is directed to recovering energy. If the concentration or purity of the VOC is sufficiently great and they are suitable to operate an Energy Conversion Device (ECD), they may be directly supplied to the ECD. In other cases, these dilute hydrocarbon concentrations are sometimes insufficient in their energy content to efficiently operate an ECD. ECDs include devices that convert chemical energy into electrical or kinetic energy such as combustion engines (internal or external), Stirling cycle engines, gas turbines, or fuel cells. In other situations, the waste gas stream has sufficient energy content to operate an ECD, but the form of the hydrocarbon is such that the ECD requires extensive modification to operate using the waste gas directly. For example, the waste gas may include complex hydrocarbons of varying concentrations or particulates. These gases may harm the ECD if they are not treated or converted to reformate.
Manufacturing processes that produce waste gas streams with a dilute hydrocarbon concentration are currently flared or burned or supplied to an ECD as part of the combustion air. Flaring the waste gas does not return any energy. Burning the waste gas produces heat. Recovering electrical or kinetic energy is generally much more valuable than recovered heat energy. GB patent application 2364257, published Jan. 1, 2002, and incorporated herein by reference, splits a gas stream having VOC into two streams. The first stream is directed to the combustion air intake of an engine and the second stream is directed to a combustion unit. Exhaust heat from the engine mixes with and combusts the second stream. This reference neither teaches concentrating the VOC nor directing the VOC to the fuel intake of the engine. WO9530470, published Nov. 16, 1995, and incorporated herein by reference, teaches a device to burn VOC in an engine by having two adsorption/desorption units so that the waste gas stream and engine may operate independently of one another. The first unit may collect and concentrate VOC as needed and the second unit supplies VOC to the engine as needed. This reference and the GB reference leave the VOC in the combustion air and do not feed the VOC to the fuel intake of the engine. US 2002/0100277 published Aug. 1, 2002, and incorporated herein by reference also teaches directing VOC to an internal combustion engine, but the VOC is not concentrated by a device. Their concentration is based on the vapor pressure of the VOC in the container. VOC not directed to the engine are condensed into a liquid by a chiller, but these liquefied VOC is not supplied to the engine as a fuel. None of these references teach reforming the concentrated VOC.
It is known that waste gases can be directly supplied to the combustion or exhaust air of an engine. One commercially available system supplies waste gases from an industrial operation to a turbine engine. In a paper by Neill and Gunter, VOC Destruction using Combustion Turbines, published September 2002, and incorporated herein by reference, describes a device that combines waste VOC with natural gas to operate a gas turbine. The gas turbine produces electricity for the facility. The waste gases come directly from the exhaust air of the industrial operation and are supplied to the engine as part of the combustion air. The turbine engine has a separate fuel source to supply the majority of the fuel. The exhaust air provides a relatively low (200 to 5000 ppm of unburned hydrocarbons and VOC) percentage of the energy content needed to operate the engine. Devices like this require an external fuel supply as part of the normal operation of the device. The external fuel supply is not merely a part of start-up or load leveling operation. These references teach directly supplying VOC to the engine without filtering or reforming and require an engine capable of consuming the VOC. By directing the VOC to the combustion air, a very large engine/generator is needed. The example given in Neill and Gunter is a 20 MW turbine to abate 150,000 Standard Cubic Feet per Minute (scfm) of air.
U.S. Pat. No. 5,451,249, issued Sep. 19, 1995, and incorporated herein by reference, teaches a device and method to supply a gas stream from a landfill to be used as the fuel source of a fuel cell. The natural gas component of the landfill gas is desirable and the VOC contained in the landfill gas is removed and is not used to supply fuel to the fuel cell. The U.S. Pat. No. 5,451,249 patent, describes heavy hydrocarbons as contaminant fractions that must be removed from the gas stream prior to reforming. Rather than teaching that the VOC is a contaminant, the present invention utilizes these hydrocarbons as the feedstock for the reformer.
The present invention is directed to a device and method to utilize the energy from waste VOC by converting the VOC into reformate for easier processing by the ECD. The present invention is capable of producing higher value kinetic or electrical energy from waste gases. The dilute VOC gas stream are organic compounds that evaporate readily into air may contain straight chain, branched, aromatic, or oxygenated hydrocarbons. The invention has the dual advantage of abating the hydrocarbons while producing electricity. More specifically, the dilute VOC presently considered waste products are reclaimed from the gas stream and used to generate electricity in a fuel cell, or via an internal or external combustion engine, a Stirling cycle engine, a gas turbine or another ECD that can produce electricity or kinetic energy. The invention is an energy efficient method to utilize the hydrocarbons entrained in the gas stream present in, or exhausted from, manufacturing, industrial, agricultural, environmental, or refinery processes.